Hello GS,
If you are going to take this one instance of trying to be responsive to someone and make a stab at trying to relate normally to a sick person, and use it to berate yourself and belittle your own progress, just stop it right there.
You have make enormous leaps since first coming up here, and it may be too soon to test anything out by seeing your father, but it may just be ok. You may have the skills to distance and deal with him now. Worst case scenario is that it sets you back somewhat, but that is something you can overcome and live to learn from it.
I still maintain contact with my N mother, because I learn something from her each time - some new memory or dynamic I hadn't noticed, some mew facet of my own behaviour that springs directly from her and I'll need to weed it out. I would feel guilty to cut her off and not look after her in some fashion. I also think that in tiny doses, it is good for my children to see her behaviour and my responses. They know they have family, even if it is a dysfunctional person, and they also know there are ways to deal with these people without becoming engulfed.
So go ahead and have dinner, and put that whipping stick away. Bon appetit!
a stern
Plucky